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snapped cam belt - but why?


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had a cam belt change earlier this year and driving home yesterday the engine just died on me. Really embarrassing because I had a film crew with me who then decided to film me having to tow the damn thing back home!

Anyway a quick check under the rocker cover confirmed that I had 3 broken rockers and 4 bent push rods. Took the front cover off and found the belt snapped with fluff galore.

What would cause such rubbing and failure?

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Fluff, and the groove worn on the belt, shows that something's been running out of alignment and the belt's been rubbing against the sides of the tensioner or one of the pulleys.

There was a service bulletin about this a long time back: there were redesigned tensioners and a different design of flange on the pulley to stop the belt 'wandering'. Yellow paint-spots were applied to the cambelt-casing of those engines who'd had this work done under warranty by a LR dealer.

From what I can see, your bottom pulley lacks the outer flange, suggesting it's the older unmodified type.

Modded type looks like this: http://forums.lr4x4.com/uploads/1153414939/med_gallery_2_134_111609.jpg

I wonder if your cambelt-changer used an old-stock kit that didn't have the modified pulley/tensioner included? Or assumed the work had already been doneso didn't need to fit the full kit?

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Did they just swap the belt, or use a standard full belt, pulley-and-tensioners service kit? You're suggesting you supplied just-the-belt not the full belt-service kit.

Any competent LR mechanic would have known about the bottom-pulley issue and wouldn't have let a vehicle out of his workshop without doing the proper job: it's something like 15 years back when this first was recognised as a major failure-mode.

The tensioners in your picture don't exactly look 'recently replaced' either.

I'd suggest visiting your supposed "LR Mechanic" accompanied by a couple of well-hungry Rhodesian Ridgebacks and an enema-syringe full of honey.

"Fix this, or you choose between outrunning the dogs over 50 miles or a honey-enema then a weekend staked-out on a local anthill".

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Sadly we are a little bit distant from a true LR Mechanic (about 700km away!) and very much in a rural area so we have to take what we can get in terms of mechanics. I have ordered a full tensioner pulley kit so that we can replace the old stuff and put in the modified pulley.

Should any member of this forum want to come out to rural Zambia and stay in a place less than a kilometre from the South Luangwa National park and stay with us and fix a couple of Landies let me know. Next major project is a replacement cross member of the 90.

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It does have the old kit fitted but it might also have been incorrectly tensioned. That would also make it ride forward and wear. As well as the modified tensioner and bottom pulley they also reduced the tension on the belt as part of 'the fix'

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The original crank sprocket (that's is in your picture), had a guide washer spot welded to it to keep the belt in line. The spot welds had a habit of breaking, and the loose washer would then damage the belt or cause it to fail. When the timing cover is removed, the washer is usually lying in the bottom of the timing chest, but it's not there, so someone removed it (the guy that replaced your belt perhaps). The one in Tanuki's picture is the better replacement that doesn't fail. With washer missing, the belt will drift outwards and rub against the timing cover, where it gets thinner and eventually snaps. The fact that you supplied the belt only means that the guide wheel/ tensioner and sprocket were not replaced, but the mechanic may well have known that the washer had come off, and should have advised you of it. If you want to get another 70 - odd, 000 miles out of the engine, then you need to replace crank sprocket, O-ring, crank seal, dust seal, gasket, fibre washer, tensioner/idler assembly, belt (Dayco or other OE spec make) and timing cover gasket.

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Do it yourself - http://forums.lr4x4.com/index.php?showtopic=22319

Les.

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Les in the case of the original 300 kit there was no washer welded to crank sprocket, that was part of the fix that Land Rover did and at the same time they changed the tensioner to have no lip on the wheel. In the OP's picture you can see the tensioner pulley has the lip which means it's from an old timing kit and the crank pulley would not have had a washer.

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No worries Les, you know far more about Land Rovers than I ever will .... I just happened to have spent too much time geeking out about 300 tdi timing kits when I first got mine. (which turned out to have the early kit the same as the OP's and lots of fluff)

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Lol, my words on removing the cover were slightly less polite considering I'd been told that had been replaced about 1000 miles before.

The new style sprocket fits and you change the tension pulley for the lipless style as well, IIRC you also have to change the mounting stud for the tension set up and do a little chamfer on the hole.

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Loosely on the subject, does anybody have any recommendations on a beam torque wrench for doing the tensioner? I have a draper one, but it's designed for far higher torques than this which makes it hard to get it accurate.

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Loosely on the subject, does anybody have any recommendations on a beam torque wrench for doing the tensioner? I have a draper one, but it's designed for far higher torques than this which makes it hard to get it accurate.

Mine is same as yours and to be honest i've done it 5 or 6 times and never had an issue. It it looks about right its right.

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Can any one tell me which make of pulley tensioner is best??? I remember some one saying that an aftermarket brand was better made than the LR one due to the welding, but cant remember which or find the thread it was mentioned in

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Can any one tell me which make of pulley tensioner is best??? I remember some one saying that an aftermarket brand was better made than the LR one due to the welding, but cant remember which or find the thread it was mentioned in

It's the crank pulley that is the one where the aftermarket is better, oem has the flange/rim spot welded on, bearmach and possibly others have the pulley and rim cast as one piece.

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